the.com/fling

means A brief, passionate romantic or sexual affair undertaken without expectation of lasting commitment.

from From Middle English 'flingen,' meaning to throw or hurl oneself with force — think of flinging an object (or your whole body) recklessly through the air. The sense of 'a short spell of self-indulgence' emerged by the 1800s, as in 'have a fling,' imagining a person literally flinging themselves into pleasure, caution thrown to the wind right along with them. The romantic/sexual sense followed naturally — a fling is a fling because you hurl yourself into it, not because you plan where you'll land.